Thermographic method of spirit duplication and transfer sheet for use therein

ABSTRACT

A transfer sheet for use in a thermographic transfer process in which the color forming component of the transfer material is a tetrakis(p-dimethylaminophenyl)ethylene salt. The salt is initially infrared translucent, but upon heating darkens to a substantially black color. Copy sheets, carrying solventtransferred salt from a thermographically produced master, are heated to darken the salt, thereby producing black on white copies.

United States Patent n 1 Bruck 1 Feb. 20, 1973 [54] THERMOGRAPHIC METHOD OF SPIRIT DUPLICATION AND TRANSFER SHEET FOR USE THEREIN [75] Inventor: Peter Bruck, Encino, Calif.

[73] Assignee: Bell 8: Howell Company, Pasadena,

Calif.

[22] Filed: Oct. 12, 1971 [21] Appl. No.: 188,271

[52] US. Cl. ..10l/469, 101/470, 101/471, 250/65 T, 117/36.2, 117/368 [51] Int. Cl. ..B41m 5/00, B410 l/06, 1341!! 5/00 [58] Field of Search ..l17/36.2, 36.8; 250/65 T; 101/469, 470, 471, DIG. l

[56] References Cited UNITED STATES PATENTS 2,755,202 7/1956 Balon et a1 ..101/D1G. 1

4/1960 Francis et a1. ..'....101/470 x 3,183,833 5/1965 Block ..101 471 OTHER PUBLlCATIONS Primary Examiner-David Klein Attorney-Nilsson, Robbins, Wills & Berliner [5 7] ABSTRACT 17 Claims, 5 Drawing Figures PATENTEU P53201975 3, 717, 093

417 INVENTOR.

THERMOGRAPHIC METHOD OF SPIRIT DUPLIC ATION AND TRANSFER SHEET FOR USE THEREIN FIELD OF THE INVENTION The field of art to which the invention pertains includes the field of planographic printing processes utilizing thermographic transfer techniques.

BACKGROUND AND SUMMARY OF THE INVENTION Duplicating processes involving thermal transfer of heat-sensitive material are well known to the prior art. For a detailed discussion of various duplicating processes utilizing thermal transfer, reference may be made to U.S. Pat. Nos. 3,122,997 and 3,122,998 issued to Raczyinski et al. Typically, an original to be duplicated is assembled with a transfer sheet substrate carrying a fusible or plasticizable layer of heat-sensitive material and a master sheet having its receiving surface in contact with the layer of fusible material. The image on the original document must be defined by an infrared absorptive material such as carbon, heavy metal or certain organic compounds so that the image areas of the original document, upon exposure, will absorb more infrared radiation than the surrounding nonimage areas. The absorbed infrared radiation is converted to thermal energy forming a thermal pattern in the original document which corresponds to the visible image pattern. This heat pattern is conducted through the substrate of the transfer sheet to the heat-sensitive layer. The heat-sensitive layer is selectively fused in correspondence to the image and the fused material is transferred to the receiving surface of the master sheet.

The position and facing of the original document relative to the transfer and receiving sheets can be varied depending upon whether a right-reading or a laterally reversed reading image is desired on the master sheet. Following image transfer, depending upon the manner of placement of the original document, the master sheet itself may serve as a facsimile copy of the original document or may be utilized as a master in a solvent duplicating process. Accordingly, the heat-sensitive layer of the transfer sheet contains, in addition to the fusible material, the necessary components for the ultimate application of the transferred image. For example, in prior art solvent duplicating processes, the heat-sensitive material contains wax, or other fusible substance, mixed with an alcohol soluble dye to produce the image color in the ultimate copy. The waxy material is thermally transferred in reverse reading fashion to the image-receiving surface of the master. The master is placed on the drum of a duplicating machine and contacted with a succession of sheets of copy paper previously wet with a volatile alcohol solvent for the dye. The solvent dissolves part of the dye in the master image and transfers it to the copy paper.

Although such a thermographic method offers many important advantages over the manual method of typing a master sheet, it also gives rise to many problems because of the tendency of coloring dyestuffs to absorb infrared radiation to some degree and convert it to heat. Unless the amount of applied radiation is controlled within close limits, the transfer material becomes heated throughout and excess material is transferred to the master sheet. In order to minimize these problems the art has avoided the use of black coloring material in the transfer layer, or any color which would tend to absorb substantial quantities of infrared radiation. The result is that solvent duplication 5 copies from the thermographically produced master are formed in low infrared-absorbing hues, such as violet.

A number of variations on the basic solvent duplication process are available or have been suggested. In one process, the transferred image material contains a chemical reagent which reacts with a second reagent on the copy paper to yield a color. The second reagent may originally be contained in the copy paper or may be delivered to the paper in the duplicator fluid applied prior to contact with the master sheet. For example, dye intermediate can be incorporated in the transfer coating. When the coating is brought into contact with copy paper damped with a liquid containing a coupling agent, the agent will combine to form the dye. Such a process is disclosed in U.S. Pat. No. 2,784,024 to Klimkowski et al. In U.S. Pat. No. 3,230,875 to Newman, a colorless or slightly colored dye precursor is utilized which develops a bright color when contacted with an acidic substance, the acidic substance being carried by the copy sheet or solvent duplicating fluid. In U.S. Pat. No. 2,935,938 to OSullivan, a colorless complex dye or dye-forming material is incorporated in the transfer material and an oxidizing agent capable of reacting with the complex to produce a color product is incorporated in the duplicating liquid. Other disclosures of interest can be found in U.S. Pat. No. 3,149,563 to Wartman et al., U.S. Pat. No. 3,257,942 to Ritzerfeld et al. and U.S. Pat. No. 3,248,236 to Raczyinski et al. In U.S. Pat. No. 2,755,201 to Webber et al., alkalinedecolorized crystals of carbinol dyes, such as crystal violet carbinol, are incorporated in carbon paper used for impact transfer onto ordinary copy sheet. An impression is obtained which is colorless initially, but which develops a strong violet color slowly upon expo sure to the atmosphere, or more rapidly upon exposure to heat. While some of the foregoing methods can reduce infrared absorption in non-image areas of the transfer sheet, thereby producing higher resolution copies, the image formed with these processes are still not black, but are of various colors depending upon the particular dye or dye precursor utilized.

The present invention provides a transfer sheet for use in a thermographic method of duplication in which the color forming component is infrared translucent but which upon transfer to the copy sheet and development yields a substantially black color. In accordance with this invention, the color forming component of the transfer sheet is a tetrakis(p-dimethylaminophenyl)ethylene salt. Such salts are initially green or nonblack color and do not absorb substantial amounts of infrared radiation, but when heated for a short period of time at an elevated temperature darken to a substantially black color. The time-temperature level of such conversion is generally above the level of time-temperature exposure to infrared radiation necessary for imagewise thermographic transfer from the transfer sheet to the master sheet. Although any tetrakis(pdimethylaminophenyl)ethylene salt is contemplated some specific salts which can be mentioned as exemplary are those in which the anion is a halide, tri-halide,

nitrate, perchlorate, sulfate, phosphate or carboxylic acid ion. Sulfonated salts are also contemplated.

In using the term substantially black in referring to the heat generated color obtained from the tetrakis(pdimethylaminophenyl)ethylene salt, a color is referred to which is black in shade, but which does not necessarily include total absorption of all wavelengths of visible light. Thus, the term refers to material which may be perceived as having a chroma but which is black shaded, so that the dominant appearance is black.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a master sheettransfer sheet-original document assemblage in accordance with the present invention;

FIG. 2 is a schematic representation in cross-section of the assemblage of FIG. 1 during infrared exposure;

FIG. 3 is a schematic representation in cross-section of the master sheet subsequent to image transfer;

FIG. 4 is a schematic representation in cross-section of the master sheet and a copy sheet during solvent transfer; and

FIG. 5 is a schematic representation in cross-section of the copy sheet during heat conversion to a substantially black image.

DETAILED DESCRIPTION As required, detailed illustrative embodiments of the invention are disclosed herein. However, it is to be understood that these embodiments merely exemplify the invention which may take many forms radically different from the specific illustrative embodiments disclosed. Therefore, specific structural and functional details are not to be interpreted as limiting, but merely as a basis for the claims which define the scope of the invention.

Referring to FIG. 1, a sandwich" assembly is illustrated which includes a base sheet 12 of relatively thick paper which supports an original document 14 to be duplicated, a transfer sheet 16 and an image-receiving, master sheet 18. The original document 14 contains infrared-absorptive indicia or images 20 on its face and is placed face-up on the base sheet 12, beneath the relatively thin transfer sheet 16. The transfer sheet 16 includes a plastic substrate 22 which carries a thin layer of heat-plasticizable or fusible material 24 on the side opposite the original document 14. The fusible material 24 contains a tetrakis(pdimethylaminophenyl)ethylene salt as will hereinafter be described in more detail. The master sheet 18 is disposed with its image receiving surface 26 adjacent the transfer sheet layer 24 of heat-sensitive material. The top edges of the transfer sheet 16 and master sheet 18 are secured by adhesive or the like to the top edge 28 of the base sheet 12.

Referring additionally to FIG. 2, there is shown a more detailed view of the disposition of the components of the assemblage illustrated in FIG. 1. As indicated, the original document 14 is placed on the supporting base sheet 12 with its infrared-absorptive indicia facing upwardly. Such indicia is constituted of carbon, heavy metal, or any material which upon exposure will absorb more infrared radiation than the surrounding non-image areas, so as to convert the absorbed infrared energy to a thermal pattern corresponding to the visible image pattern on the document 14. The transfer sheet substrate 22 can be formed of Mylar (a transparent, tensilized polyethylene glycol terephthalate polyester film) which is sufficiently thin, about 0.5 mil, to avoid significant attenuation of the conducted heat pattern. The master sheet 18 is also formed of material which is transparent to infrared radiation and can be formed of Mylar, polypropylene, polyethylene, or the like. Since the master sheet 18 must be sufficiently strong to withstand a large number of impacts during subsequent duplication, it is made relatively thick, about l-2 mils.

The assemblage of base sheet 12, document 14, transfer sheet 16 and master sheet 18 is sandwiched together under pressure so that directly opposing surfaces are contiguous with one another. The assemblage 10 is exposed to radiations 30 rich in infrared, directed onto the master sheet 18 so as to penetrate the master sheet 18 and transfer sheet 16 and impinge onto the original document 14. The radiation 30 generates a temperature rise in the image portions 20 of the document 14 resulting in a thermal pattern emanating from the document 14. For example, utilizing a 1,000 Watt tungsten lamp as the infrared source, the heat-sensitive transfer material 24 is selectively fused to a softened, plasticized condition in regions 32, indicated by dashes, corresponding to the indicia 20. As is well known, the exposure time required is a function of the materials involved and the intensity of radiation.

Referring additionally to FIG. 3, after the infrared radiation exposure has been terminated, the imaged master sheet 18 may be removed from the assemblage 10 and will carry the fused regions 32 of the transfer layer 24 away from the transfer sheet 16. In the assembly shown, the solidified fused material 32 is transferred in mirror image fashion and thus the master sheet 18 would be used to produce right-reading copies.

Referring now to FIG. 4, there is depicted the stage of duplication wherein solvent has been applied to a sheet of copy paper 34 which thereafter has been pressed into contact with the imaged portions 32 of the transfer layer as carried by the master sheet 18. The solvent penetrates only partially into the copy paper 34, as indicated by the line 36, and carries with it color forming component 38 dissolved therein from the imaged portions 32. The master sheet 18 is thereafter removed from contact with the copy sheet 34.

Referring to FIG. 5, the copy sheet 34 carrying information in the form of solvent transferred color component 38 is placed on a heated platen 40 whereupon it is heated to a temperature sufficient to convert the tetrakis(p-dimethylaminophenyl)ethylene salt to a substantially black color, thereby producing a black-color copy of the information indicia 20 on the original document 14. This heat step is conducted at a temperature of about -150 C for a time sufficient to cause the conversion to the black color, about I 10 seconds. The thermographic transfer step results in heating of the transferred image portions 32 but at a generally lower level, about 50 C as a maximum. While this may be sufficient to somewhat darken the color forming salt, generally a temperature of at least 75 C over a period of at least seconds is required to obtain sufficient darkening to produce a black appearing color. In place of the plate n 40, one can impinge radiation rich in infrared directly onto the imaged surface of the copy sheet 34, the amount of radiation being absorbed by the imaged areas 38 thereon increasing as the imaged areas 38 darken. However, a substantially longer exposure time to the infrared radiation is required than is needed when the copy sheet 34 is simply passed over a heated platen 40 maintained conveniently at about l-l 50 C.

The heat-sensitive layer 24 is about 0.2-0.6 mil thick and is formed of a combination of heat plasticizable transfer material as known to the art and a color forming component. The color forming component is initially substantially infrared translucent but, upon exposure to relatively high levels of heat, darkens to a substantially black color. In accordance with the present invention, the color forming component is a tetrakis(pdimethylaminophenyl)ethylene salt. The fusible portion of the heat-sensitive layer 24 can be any of the generally available commercial materials such as described in Raczyinski et al. or other patents referred to above. Such compositions, referred to by the art as carbons," typically are formulated of waxy materials in various combinations including carnauba wax, microcyrstalline wax, paraffin wax, ozokerite, spermacetti wax, beeswax, montan wax, synthetic waxes such as Carbowax (a high molecular weight polyethylene glycol) and the like, alone or in combination with softening agents. Softening agents include oils such as Red Z oil, vegetable oils such as castor oil, animal oils such as lanolin, fatty acids and the like. Modifications to improve strength of film forming characteristics may include the addition of small amounts of polyethylene, polybutylene and other polymeric compounds formed of unsaturated aliphatics and/or other modifying materials compatible with the waxy substances to form a stable composition. The composition provides for a continuous layer capable of thermographic transfer to surfaces in contact therewith and which has slight solubility in the duplicating solvents utilized so as to continuously cleanse the surface of the imaged master during production of copy.

It is desirable to embody as high a concentration of the color forming component as possible in the carbon coating consistent with the ability of the coating to maintain the desired film characteristics and strength. Generally, the amount of color forming component introduced as an ingredient in the coating composition depends on the ability to maintain sufficient fluidity under the conditions of coating to achieve a desired application and coverage. It is advisable to maintain a concentration of the color forming component of about 50-75 percent by weight. In general, fluidity characteristics fall off when the concentration reaches 75 percent by weight but more may be used with the introduction of fluidizing agents.

Referring more specifically to the color forming components, the tetrakis(p-dimethylaminophenyl)ethylene salt has a generally deep green color when in pure form and has the formula wherein when n is l, X is a divalent anion, and when n crystal violet, but can be increased by applying the solvent at an increased temperature, such as at 50-60 C and/or by utilizing a more strongly solubilizing material, such as acetone or methyl ethyl ketone, alone or in mixture with methanol or the like.

The preparation of various tetrakis(pdimethylaminophenyl)ethylene salts are well known to the art. Typically, the dinitrate is prepared and the other salts are prepared from the dinitrate by dissolving the dinitrate in water and precipitating the desired salt by adding the desired anion in stoichiometric excess. For example, a sodium salt of the anion can be added and the new salt precipitated, if necessary by colling the solution until precipitation. The dinitrate salt can be prepared by shaking tetrakis(p-dimethylaminophenyl)ethylene with silver nitrate. Reference can be made to a communication by DH. Anderson et al., Journal of the American Chemical Society, Vol. 83, pages 3,157-3158 (I961), Elofson et al. Some Reactions of Solid Tetrakis(p-dimethylaminophenyl)ethylene Diiodide Monohydrate, Journal of the American Chemical Society, Vol. 85, pages 2,622-2624 and a paper entitled Electron Spin Resonance Studies of A Weakly Coupled Biradical by Anderson et al. reported at the 1960 spring meeting of the American Physical Society, Bulletin American Physical Society 227, Series II, Vol. 5 1960).

In addition to the foregoing compounds, the present invention comprehends the use of sulfonated tetrakis(p-dimethylaminophenyl)ethylene salts wherein from one to four of the phenyl groups have the transfer sheet substrate. The following examples, in

which all parts are by weight, will illustrate various aspects of the invention.

EXAMPLE I To 90 parts of toluene are added 10 parts of carnauba wax, 5 parts of Carbowax 6,000 (a high molecular weight polyethylene glycol) and 2.5 parts of tetrakis(pdimethylaminophenyl)ethylene dinitrate. The mixture is ball-milled for hours and then coated on an 0.5 mil thick Mylar substrate to a dry coating 0.5 mil thick to constitute a transfer sheet in accordance with this invention. An original document to be copied is placed face-up beneath the transfer sheet and a master sheet is placed with its receiving surface in contact with the coating on the transfer sheet. Thermal exposure is made utilizing a spirit process exposure and printing unit sold by Bell & Howell Company under the trademark Ditto Combomatic. Exposure settings on this machine run from a high exposure of l to a low expo sure of 10. In this example, exposure is made at a setting of 7.0 to obtain image-wise transference of the carbon to the master sheet. The master sheet is placed in a Combomatic and duplicate copies are made on Dittcopy copy paper using methanol duplicating solvent. The copy paper is heated at about 120 C for several seconds to yield copies which appear substantially black.

Copies of greater image density are obtained by heating the duplicating solvent to about 50 C and applying it at that temperature to the copy paper just prior to contact with the master.

EXAMPLE II A carbon composition was coated on a Mylar substrate from a ball-milled toluene solution containing as the major components equal parts of tetrakis(pdimethylaminophenyl)ethylene dinitrate and an approximately 2:1 mixture of carnauba wax and Carbowax 6000. A master was formed as in Examplel and copies on Dittcopy paper were made. The Dittcopy paper was heated for several seconds on a rotating drum heater at about 120-1,500 C to produce substantially black copies of the original document.

Images of increased density can be obtained by substituting methyl ethyl ketone for the methanol duplicating solvent.

EXAMPLE III A carbon composition was coated on Mylar substrate from a ball-milled toluene solution containing as the major components equal parts of tetrakis(pdimethylaminophenyl)ethylene di-tri-iodide and an approximately 2:1 mixture of carnauba wax and Carbowax 6000. A master was formed as in Example I and copies were made on Dittcopy paper. The copies were heated as described in Example I] to yield substantially black images.

EXAMPLE IV Tetrakis(p-dimethylaminophenyl)ethylene dinitrate is dissolved in water and a stoichiometric excess of sodium acetate is added to precipitate tetrakis(pdimethylaminophenyl)ethylene diacetate. The diacetate salt is utilized as in Example I in place of the dinitrate salt to produce substantially black copies.

EXA'IZFLE Tetrakis(p-dimethylaminophenyl)ethylene dinitrate is dissolved in water and a stoichiometric excess of sodium p-nitrobenzoate is added to precipitate tetrakis(p-dimethylaminophenyl)ethylene di-pnitrobenzoate. The p-nitrobenzoate salt is utilized as in Example I in place of the dinitrate salt to produce sub stantially black copies.

In like manner to the foregoing, one can synthesize and utilize iodide-triiodide, diperchlorate, dibromide, dichloride, ditribromide, sulfate and phosphate salts of tetrakis(p-dimethylaminophenyl)ethylene, and utilizing them in the manner of Example I, produce substantially black copies.

The embodiments heretofore illustrated were described in the context of a solventor spirit duplica' tion process of a specific type in which copy paper wet with solvent is brought into contact with a master sheet. However, master sheets thermographically imaged in accordance with the invention may be used to produce duplicate copies by means other than this specific duplication process. For example, the imaged masters may be superposed with their images and surfaces in contact with a solid, heat-meltable coating on a copy sheet and subjected to heat or infrared radiation to cause the copy sheet coating to melt and dissolve some of the color forming salt from the master image to form a duplicate copy. Suitable copy sheet coatings are those based upon solid materials which, in their melted form, are solvents for the color forming component. Examples are cetyl alcohol, stearyl alcohol, stearic acid, palmitic acid, and the like. The thermographically obtained master sheet can also be utilized in a gelatin system in which the image is transferred from the transfer sheet in right-reading fashion by modification of the position and facing of the original document. The image is then transferred from the master sheet by absorption, during contact, into a gelatin compound disposed in a pan in which a succession of copy sheets can be placed to obtain duplicate images of the original, and then made substantially black by heating of the copy sheets.

I claim:

1. In a transfer sheet for use in a thermographic method of placing an image on a receiving sheet, said transfer sheet comprising an infrared-translucent base sheet carrying transfer material for thermographic transfer therefrom, said transfer material containing a color forming component, the improvement according to which said color forming component is a tetrakis(pdimethylaminophenyl)ethylene salt.

2. The invention according to claim 1 wherein the anion of said salt is a halide, tri-halide, nitrate, perchlorate, sulfate, phosphate or carboxylic acid ion.

3. The invention according to claim 1 wherein said salt is a tetrakis(p-dimethylaminophenyl)ethylene dinitrate.

4. The invention according to claim I whereas said salt is a tetrakis(p-dimethylaminophenyl)ethylene diiodide.

5. The invention according to claim I wherein said salt is a tetrakis(p-dimethylaminophenyl)ethylene dichloride.

6. The invention according to claim 1 wherein said salt is a tetrakis(p-dimethylaminophenyl)ethylene dibromide.

7. The invention according to claim 1 wherein said salt is a tetrakis(p-dimethylaminophenyl)ethylene ditribromide.

8. The invention according to claim 1 wherein said salt is a tetrakis(p-dimethylaminophenyl)ethylene ditriiodide.

9. The invention according to claim 1 wherein said salt is a tetrakis(p-dimethylarninophenyl)ethylene iodide-triiodide.

10. The invention according to claim 1 wherein said salt is a tetrakis(p-dimethylaminophenyl)ethylene sulfate.

11. The invention according to claim 1 wherein said salt is a tetrakis(p-dimethylaminophenyl)ethylene phosphate.

12. The invention according to claim 1 wherein said salt is a tetrakis(p-dimethylaminophenyl)ethylene acetate.

13. The invention according to claim 1 wherein said salt is a tetrakis(p-dimethylaminophenyl)ethylene di-pnitrobenzoate.

14. The invention according to claim 1 wherein the cation of said salt is sulfonated.

15. A thermographic method of spirit duplication, including to steps of:

' assembling (l) a transfer sheet comprising a base sheet carrying a heat-plasticizable coating of spirit duplicating transfer material containing an infrared translucent color forming component which darkens to a substantially black color upon heating said color-forming component comprising a tetrakis (p-dimethyl-aminophenyl) ethylene salt, (2) a master sheet having a receiving surface in contact with said transfer material and (3) an original sheet bearing thereon infrared absorbing, heat-generating image areas;

heating said assemblage to a temperature below the temperature at which said color forming component substantially darkens but sufficient to plasticize said transfer material in areas corresponding to said image areas to transfer said plasticized material to said master sheet receiving surface;

separating said master sheet from said transfer sheet;

providing a copy sheet;

solvent transferring portions of said color forming component to said copy sheet to form an image thereof on said copy sheet; and

heating said imaged copy sheet to a temperature high enough to darken said color forming component to a substantially black color.

16. The invention according to claim 15 wherein the anion of said salt is a halide, tri-halide, nitrate, perchlorate, sulfate, phosphate or carboxylic acid ion.

17. The invention according to claim 15 wherein the cation of said salt is sulfonated. 

1. In a transfer sheet for use in a thermographic method of placing an image on a receiving sheet, said transfer sheet comprising an infrared-translucent base sheet carrying transfer material for thermographic transfer therefrom, said transfer material containing a color forming component, the improvement according to which said color forming component is a tetrakis(p-dimethylaminophenyl)ethylene salt.
 2. The invention according to claim 1 wherein the anion of said salt is a halide, tri-halide, nitrate, perchlorate, sulfate, phosphate or carboxylic acid ion.
 3. The invention according to claim 1 wherein said salt is a tetrakis(p-dimethylaminophenyl)ethylene dinitrate.
 4. The invention according to claim 1 whereas said salt is a tetrakis(p-dimethylaminophenyl)ethylene diiodide.
 5. The invention according to claim 1 wherein said salt is a tetrakis(p-dimethylaminophenyl)ethylene dichloride.
 6. The invention according to claim 1 wherein said salt is a tetrakis(p-dimethylaminophenyl)ethylene dibromide.
 7. The invention according to claim 1 wherein said salt is a tetrakis(p-dimethylaminophenyl)ethylene di-tribromide.
 8. The invention according to claim 1 wherein said salt is a tetrakis(p-dimethylaminophenyl)ethylene di-triiodide.
 9. The invention according to claim 1 wherein said salt is a tetrakis(p-dimethylaminophenyl)ethylene iodide-triiodide.
 10. The invention according to claim 1 wherein said salt is a tetrakis(p-dimethylaminophenyl)ethylene sulfate.
 11. The invention according to claim 1 wherein said salt is a tetrakis(p-dimethylaminophenyl)ethylene phosphate.
 12. The invention according to claim 1 wherein said salt is a tetrakis(p-dimethylaminophenyl)ethylene acetate.
 13. The invention according to claim 1 wherein said salt is a tetrakis(p-dimethylaminophenyl)ethylene di-p-nitrobenzoate.
 14. The invention according to claim 1 wherein the cation of said salt is sulfonaTed.
 15. A thermographic method of spirit duplication, including to steps of: assembling (1) a transfer sheet comprising a base sheet carrying a heat-plasticizable coating of spirit duplicating transfer material containing an infrared translucent color forming component which darkens to a substantially black color upon heating said color-forming component comprising a tetrakis (p-dimethyl-aminophenyl) ethylene salt, (2) a master sheet having a receiving surface in contact with said transfer material and (3) an original sheet bearing thereon infrared absorbing, heat-generating image areas; heating said assemblage to a temperature below the temperature at which said color forming component substantially darkens but sufficient to plasticize said transfer material in areas corresponding to said image areas to transfer said plasticized material to said master sheet receiving surface; separating said master sheet from said transfer sheet; providing a copy sheet; solvent transferring portions of said color forming component to said copy sheet to form an image thereof on said copy sheet; and heating said imaged copy sheet to a temperature high enough to darken said color forming component to a substantially black color.
 16. The invention according to claim 15 wherein the anion of said salt is a halide, tri-halide, nitrate, perchlorate, sulfate, phosphate or carboxylic acid ion. 